Verify that absolute path is used in journal/ledgerDirectories options

[SrishT]

Description

If the user forgets to include the leading forward slash ("/") in the journalDirectories option on the bookkeeperCluster resource, then the persistent volume subpath is mounted to "/bk/journal/j0" on the bookie pod, but the journal files are written to "/opt/bookkeeper/bk/journal/j0" (path calculated relative to the bookie home folder).
As a result, the journal data is not saved to the persistent volume, so there is a danger of the local disk getting out of space and/or data being lost if the pod gets deleted.
Same problem exists with ledgerDirectories setting.

Importance

must have

Location

pkg/apis/bookkeeper/v1alpha1/bookkeepercluster_types.go

Suggestions for an improvement

Make use of the admission webhook to verify that both journalDirectories and ledgerDirectories options are using absolute paths to set the folder structure.